Given the head of a linked list, find the node where the cycle begins. If no cycle exists, return null. The list may contain a cycle, which occurs if a node can be revisited by following the ’next’ pointers continuously.
You are given the head of a singly linked list. The goal is to reorder the list such that the nodes are arranged as follows: L0 → Ln → L1 → Ln-1 → L2 → Ln-2 → …, without modifying the values of the nodes. Only the structure of the list can be changed.
Given a sorted array of integers, find two numbers whose sum equals a target value. Return the indices of these two numbers, ensuring they are 1-indexed.
A happy number is a number that eventually reaches 1 when replaced by the sum of the squares of its digits. If the process results in an endless loop of numbers, the number is not happy. Your task is to determine whether a given number is a happy number.
Given an integer array nums, move all the zeros to the end while maintaining the relative order of the non-zero elements. Perform the operation in-place without making a copy of the array.
